This invention relates to an apparatus for sterilizing a culture medium contained in a cultivating vessel such as wide-mouthed bottle for cultivating mushrooms such as hackberry or champignon by the use of heated steam.
In the case of cultivating mushrooms such as hackberries, they are normally placed in a cultivating vessel such as wide-mouthed bottle containing a culture medium consisting essentially of sawdust. For the cultivation of the mushrooms in this manner, the culture medium is preliminarily sterilized by using heated steam for preventing various germs or bacteria from breeding in the cultivating vessel and for facilitating the growth of the mushrooms.
One typical example of a conventional steam sterilizing apparatus for the mushroom culture medium of the character described above, is disclosed in Japanese Utility Model Laid-Open Publication (Kokai) No. 139232/1986 published Aug. 29, 1986. The known steam sterilizing apparatus comprises a sterilizing container usually of a box shape, a steam supply pipe connected to the sterilizing container, a boiler for supplying highly heated and pressurized steam to the sterilizing container, and an exhaust pipe for discharging the steam and air in the sterilizing container outwardly.
The steam supply pipe is equipped with a steam valve for adjusting the amount of supply of the steam into the container body, and the exhaust pipe is also equipped with an exhaust valve for adjusting the exhaust amount of the steam from the sterilizing container. A drain pipe is also disposed at the bottom of the sterilizing container having one end opening into the container for draining water condensed therein, and the drain pipe is equipped with a trap therein.
The steam sterilizing apparatus of this conventional type operates as follows. Highly heated and pressurized steam is supplied into the sterilizing container from the boiler through the steam supply pipe with the steam valve opened and the exhaust valve also opened, until the temperature in the sterilizing container rises to about 100.degree. C.
After the temperature has been raised to about 100.degree. C., the steam is continuously supplied for a period of time with the exhaust valve opened, this process usually being called a "flow-steaming process" to exhaust the air in the sterilizing container. After the flow-steaming process, the exhaust valve is closed to increase the internal pressure of the sterilizing container and to thereby increase the inner temperature to about 120.degree. C. required for sterilizing the culture medium placed beforehand in the sterilizing container. Since the pressure in the sterilizing container is kept constant by means of a pressure adjusting valve, the temperature therein can be constantly kept at about 120.degree. C. as long as the supply of the steam is continuously made with the exhaust valve closed. This process is a socalled "sterilizing process", and after completion of the sterilizing process carried out from a predetermined period of time, the steam valve and the exhaust valve are both closed to gradually reduce or lower the pressure and the temperature in the sterilizing container, this process being a so-called "settling process". The steam remaining in the sterilizing container is then exhausted into the atmosphere by opening the exhaust valve.
During these processes, a part of the steam supplied in the sterilizing container contacts the inner wall surfaces thereof and the culture medium and is then condensed into water, which is drained to outside the sterilizing container through the drain pipe equipped with the trap. The condensate, i.e. water, however, often includes much sawdust or other substances such as dirt. In case such condensate is drained as it is, the sawdust or other substances will be caught by the trap to finally clog it, and result in difficulty in draining the condensate through the drain pipe, and in certain extreme cases, the bottom of the sterilizing container is flooded with the condensate.
In the above described apparatus, it is not so difficult to raise the temperature in the sterilizing container to about 100.degree. C. in the summer season or in a case where the sterilizing container is placed in an environment at which the temperature is relatively high, but in winter or in a case where the environment is of relatively low temperature, it is difficult to raise the temperature in the sterilizing container and the culture medium disposed therein to about 100.degree. C. by supplying the steam of about 100.degree. C., so that much time is consumed for raising and maintaining the temperature in the sterilizing process.
This difficulty may be eliminated by constructing the sterilizing container using a double-wall structure such as in medical sterilizing devices, but such structures require are costly, and are therefore not economically applicable to a sterilizing container for the culture medium for, for example, mushrooms.